I have never seen 12 ga on a receiver pack more like 16. 12 is what is used on reg 7.2 car packs it's overkill for a receiver pack and it prob won't fit onthe box. When I ran nimh I had great luck with the trinity ep or ib 1600 packs they would run for an hour and always treated me well no matter how I miss treated them they were around 25 bucks.